Constructing spin crossover-fluorescence bifunctional iron(II) complexes based on tetraphenyl ethylene-decorated AIEgens.

Investigating spin crossover (SCO)-fluorescence bifunctional materials and establishing their structure-function relationships are attractive topics in chemistry and materials science. However, it remains challenging to preserve the fluorescence and SCO properties simultaneously in aggregated solid states. Herein, we design an ( E )-2,6-bis(1 H -pyrazol-1-yl)-4-(4-(1,2,2-triphenylvinyl)styryl)pyridine (tpe-bpp) ligand, which contains coordinated SCO and fluorescence units of an aggregation-induced emission luminogen (AIEgen). The coordination of the tpe-bpp ligand with different Fe II salts generated three mononuclear complexes: [Fe(tpe-bpp) 2 ](ClO 4 ) 2 ·5.75CH 2 Cl 2 (1), [Fe(tpe-bpp) 2 ](ClO 4 ) 2 ·CH 2 Cl 2 ·3CH 3 OH (2) and [Fe(tpe-bpp) 2 ](BF 4 ) 2 ·CH 2 Cl 2 ·3CH 3 OH (3). Single-crystal X-ray diffraction studies showed that they shared a similar [Fe(tpe-bpp) 2 ] 2+ complex cation. Their counterions and co-crystallized solvents were different. Magnetic measurements revealed that 1, 2, and 3 exhibited a complete SCO behavior with the transition temperatures T 1/2 of 375, 260, and 248 K, respectively. Fluorescence measurements confirmed the existence of the AIE property for both the tpe-bpp ligand and Fe(II) complexes. A monotonic decrease of the photoluminescence (PL) intensity upon increasing the temperature was behavior observed for all three complexes.